The commercial production of resorcinol must specifically address the isomer problem. Whether starting from benzene, phenol, or non-cyclic compounds, the commercial feasibility of any resorcinol process depends upon its ability to achieve high yields of meta-oriented precursors to enable the conversion to resorcinol.
There are currently two industrial methods for the production of resorcinol, a compound typically used as a synthetic resin component of rescrcinol-formaldehyde resins for rubber and wood glue industries. There are two other routes to resorcinol which potentially could become attractive. One industrially-practiced process is the sulfonation process which is described in Chem. Eng., Sept. 25, 1967. In this process, benzene is sulfonated with oleum to establish meta-orientation (Reaction 1) and then neutralized to obtain a sodium-sulfonic acid salt (Reaction 2) which is further treated with dry caustic to eliminate the sulfonic acid group to form sodium sulfite (Reaction 3) which is then acidified to resorcinol (Reaction 4). ##STR1## In commercial practice, this process is energy intensive in obtaining dry sodium products (sodium sulfate and sodium sulfite) and is capital intensive due to the corrosion problems connected with sulfuric acid and caustic.
A second industrial process follows the diisopropylbenzene route to resorcinol. See, e.g., U.S. Pat. Nos. 4,347,393, 4,283,570, 4,283,567, 4,273,623, 4,239,921, 4,229,597 and 4,192,958. In this process, propylene is added to benzene to establish meta orientation. (Reaction 5). The para isomer and other propylated species are formed which must be separated and recycled so that high yields of pure meta-product can be obtained. Alternatively, the para isomer can be separately converted to hydroquinone. In the latter case, the process becomes a resorcinol-hydroquinone process. Subsequently, the isopropyl groups are oxidized to obtain hydroperoxide functionality (Reaction 6). This intermediate then converts to resorcinol and acetone (Reaction 7). ##STR2## The diisopropylbenzene process suffers from two major drawbacks. First, the addition of propylene to benzene is not a selective reaction so that means for handling unwanted para-isomer products must be employed. Secondly, the economics of this process are largely dependent upon the acetone market which could be a liability if there is an unexpected change in that market.
A third route to resorcinol, which may possibly become commercialized, is described in U.S. Pat. Nos. 3,862,245 and 3,862,246. This process involves the nitration of benzene (Reaction 8) to obtain the desired meta orientation. Dinitrobenzene is then reduced to phenylene diamine (Reaction 9). A substitution reaction then yields resorcinol and ammonium sulfate (Reaction 10). ##STR3##
The nitration process is expensive due to the nitration step, produces large quantities of salt, and suffers from yield losses to other isomers.
A fourth process, more recently emerging as a commercial route to resorcinol, and described in U.S. Pat. Nos. 4,397,709 and 4,250,336, involves the condensation of acetone and acrylic acid to form a delta-keto-acid (Reaction 11). This acid is then reacted with an alcohol (Reaction 12) to obtain the keto ester which can be cyclized over palladium/thorium catalyst to obtain resorcinol (Reaction 13). ##STR4##
The acetone/acrylic acid process has several drawbacks. Apparently, this process is limited in the Michael addition step due to the formation of by-product mesityl oxide. U.S. Pat. No. 4,397,709 teaches the use of a secondary amine catalyst. U.S. Pat. No. 4,250,336 teaches the combinaton of the cyclization and dehydrogenation steps (Reaction 13). The difficulty in making this process work successfully is catalyst lifetime and recycle of the mesityl oxide.
In summary, prior commercialized resorcinol processes exhibit potential market vulnerability because of co- or by-product formation and capital intensity. The present invention utilizes optimized, selective reactions which yield minimal by-products. The recognition of the intermediary of .alpha.,.beta.-unsaturated ketone enables highly selective meta-oriented reactions. Any by-products which may be produced can be conveniently recycled since they are typically substrates for some of the preceding or subsequent reaction steps. In its preferred embodiment, this process advantageously first removes aromatization, fixes the meta-regioselective hydroxyl moiety and subsequently restores aromatization. Therefore, it is an object of this invention to provide a method of manufacturing resorcinol which minimizes co-products or by-products from the reaction steps.
It is a further object of this invention to utilize highly selective reactions for each process step thereby increasing the overall yield for the process.
It is another object of this invention to practice non-corrosive reaction steps thereby reducing the level of capital investment required to construct a plant to practice this invention.
These, and further objects of the invention, will become apparent to those skilled in the art with reference to the description below.